Each year, 8 of every 1000 children born have some form of congenital heart disease which involves a malformation of a part of the heart. Approximately 10% of these cases are represented by malformations in which there is only one functional, well-formed, ventricular chamber in the heart of the infant. While most commonly described as a deficit of the right side of the heart in which the right ventricle and perhaps the right atrium are not well-formed, the deficit may occur on either side of the heart. The system for directing the venous return blood flow to the lungs for re-oxygenation and the flow of oxygenated blood to the body is severely impacted, as the blood must entirely mix within the heart. Without some form of palliative or reconstructive surgery nearly all such infants do not survive for more than a brief time. The most common treatment for this condition includes a series of surgeries commonly known collectively as the Fontan procedure. The outcome of the Fontan procedure is to direct the venous return flow of de-oxygenated blood directly into the pulmonary arteries and thence into the lungs, entirely bypassing the heart. Doing so entails relying on the central venous pressure and the negative thoracic pressure generated through inspiration to provide the motive force to move the returned blood through the lungs and into the left atrium of the heart where it begins its circulation back to the body. However, patients are enabled to live generally normal lives with proper medical care. That medical care, however, includes the high likelihood for requiring interventional access to the interior of the heart, and there are significant problems associated with gaining this access.
To better understand the problems with gaining needed interventional access to the heart, a brief discussion of the anatomy of the heart, as illustrated in the accompanying drawings, and the use of the Fontan procedure is in order. The heart H is the organ of the body which powers the circulation of blood within the body. Circulating blood within the body includes providing a sufficient flow of oxygenated blood to all parts of the body to, among other things, provide oxygen to the tissues and organs of the body. As the blood circulates within the tissues, it becomes de-oxygenated, or cyanotic, and is returned to the lungs where the blood is recharged with oxygen. The heart is a muscular organ which includes four pumping chambers to power this circulation. These chambers are the right atrium RA, the left atrium LA, the right ventricle RV and the left ventricle LV. The heart undergoes a rhythmic and sequenced contraction of first the atria and then the ventricles. It is convenient to begin the discussion with the right atrium RA. Returning cyanotic blood from the head and upper extremities enters the superior vena cava SVC, and blood returning from the lower organs and extremities enters the inferior vena cava IVC. Blood thus returned is ported from the venae cavae, SVC and IVC, into the right atrium RA. The pumping cycle of the heart begins with contraction of the right atrium RA, pressurizing blood contained therein such that the blood flows through the tricuspid valve into the right ventricle RV. Contraction of the right ventricle RV closes the tricuspid valve and forces the blood through the pulmonary valve, into the pulmonary arteries PA, and thence into the lungs. Blood passes through the lungs, primarily under the motive force of right ventricular contraction. The blood is oxygenated in the lungs and passes into the left atrium LA. Atrial contraction forces blood from the left atrium LA and through the mitral valve into the left ventricle LV. Ventricular contraction closes the mitral valve and forces the blood through the aortic valve, into the aorta A, and thence to the various parts of the body by means of the arterial system. The arterial system includes smaller arteries and capillaries allowing the blood to supply oxygen the tissues. The blood gradually becomes more cyanotic as it moves through the tissues and into the venules and larger veins of the venous system. The venous system returns the blood to the superior vena cava SVC and the inferior vena cava IVC and thence into the right atrium RA, completing a cycle. Blood moves through the venous system urged by general bodily muscle contractions which generally cyclically compress the veins. Aided by one way valves in the veins, such repeated contractions effectively push the blood back towards the heart H. Venous flow is further urged due to the continuing flow of blood from the left ventricle LV into and through the tissues by way of the arterial system. Blood pressure in the venous system is maintained generally low at least partially by the pumping action of the right side of the heart as blood is drawn into the right atrium RA from the venae cavae.
When an infant is born with certain forms of congenital heart disease, the above-described heart function and circulation is severely impacted. The functioning of one side of the heart may be severely limited or non-existent. Mediation of this condition generally involves a first surgery which provides a small arterial shunt of blood to the lungs. This provides limited but adequate blood flow for the infant to grow and for the lung vasculature to mature and be ready for a second surgery. The second surgery includes disconnecting the superior vena cava SVC from the right atrium RA and connecting the superior vena cava to the superior aspect of the right pulmonary artery PA. This procedure, known as the bidirectional Glenn procedure, thus bypasses venous return flow from the head and upper extremities directly to the lungs. The pulmonary arteries PA are completely detached from the heart such that they essentially form one bi-directional artery connected between the inlets of the lungs. The outlet from the right ventricle RV is closed. During recuperation from the second surgery, the flow from the inferior vena cava IVC is allowed to continue into the malformed heart. After a further period of growth and recuperation, a third surgery is performed in which the flow from the inferior vena cava IVC is also directed into the pulmonary artery PA. This third surgery is particularly referred to as a Fontan operation while its combination with the Glenn procedure is collectively referred to as the Fontan procedure. In this third surgery, the connection of the inferior vena cava IVC to the right atrium RA is also severed and the inlet to the right atrium is closed such that the right side of the heart is entirely disconnected from the systemic venous return flow. Also the space within the right atrium RA is made contiguous with the space within the left atrium LA. The next step of the surgery is to attach the inferior vena cava IVC to the inferior aspect of the right pulmonary artery PA, thus perfecting a return path for venous blood from the lower body to the lungs. This connection, however, cannot be done with exclusively native tissue because the two vessels (pulmonary artery PA and interior vena cava IVC) are not located in close enough proximity to each other. A synthetic, generally tubular, vascular graft is used to make this connection. Two particular procedures currently used to implant this graft are the Lateral Tunnel Fontan and the External Conduit Fontan. Both procedures entail connecting a synthetic vascular tube graft between the proximal end of the inferior vena cava IVC and the inferior aspect of pulmonary arteries PA. In the case of the External Conduit Fontan, the graft lies outside and alongside the heart, while in the case of the Lateral Tunnel Fontan the graft passes through a tunnel surgically prepared in the right side of the heart. In either case, the synthetic tubular graft conducts returning cyanotic blood from the lower body directly to the pulmonary arteries. The Lateral Tunnel Fontan and the External Conduit Fontan thus provide the same function. Physicians choose one or the other type of Fontan based on anatomical/medical considerations and institutional preference. In either case, the interior of any vestigial atrium is made contiguous with the interior of the other, well-formed, atrium. Thus, the pumping action of the heart is undertaken entirely by rhythmic and sequenced atrial and ventricular contractions. More particularly, blood flowing into the heart from the lungs is forced by atrial contraction into the well-formed ventricle. The ventricle then contracts and pushes the blood into the aorta A and thence into the arterial circulation in all areas of the body. Blood moves into tissues of the body from the arterial system and leaves those tissues by way of the venous system, returning directly to the lungs and bypassing the heart.
Management of patients who have had Fontan procedures performed on their hearts is complicated by the fact that access to the heart from the venous system is made difficult if not impossible. Such patients have a high incidence of arrhythmia and other cardiac complications, and the treatment and intervention for such complications can require later access to the heart. The common way to reach the normal heart is through the pathway provided by the superior vena cava SVC or the inferior vena cava IVC using a catheter threaded from outside the body by way of the venous system to one of those areas and thence into the heart. However, that pathway is removed by the Fontan procedure. Often surgeons will create a fenestration, or opening, connecting the graft to the interior of the heart during the Fontan procedure. This is done to lower venous pressure and to make the pressure more stable in the early post-operative period. These fenestrations are unreliable and often close soon after surgery. If, however, the fenestration remains patent, at best the patient is left with a permanent leakage of cyanotic blood through the fenestration and into the oxygenated blood being pumped to the body. The patient experiences reduced exercise tolerance along with an increased risk of embolic stroke due to clots that may form in the venous system and and flow into the systemic circulation. Thus it is generally undesirable in the long term to create a permanent fenestration at the time of the Fontan procedure. However, as mentioned above, access to the heart is often required for certain treatments, and, if no communication exists an additional surgery may be required to facilitate the access and undertake the treatment or treatments of the heart.
When the approach of making a fenestration during the Fontan procedure is taken, the fenestration may spontaneously close, often within a short time after surgery. Further, in cases in which a fenestration is not made during the Fontan procedure, or when such fenestration has later closed, some patients experience intolerable elevation of venous pressure. An elevation of venous pressure is concomitant with the Fontan procedure because the venous system is not isolated from the back pressure due to the blood flow through the lungs as would be the case with a normal heart. Although tolerable in most cases, as mentioned above, in other cases complications can arise. These complications often include the collection of fluid in the chest and abdominal areas or malabsorption of nutrients from the gut. The indicated procedure in such cases is to intervene surgically to make or re-open a fenestration to, in effect, create a pressure relief to allow a bleed-off of venous blood from the graft into the heart and thus reduce the pressure. This procedure makes the patient more cyanotic at baseline, compromises the patient's exercise tolerance, and increases stroke risk. However, it may be considered acceptable as compared to the longer term effects of symptomatically elevated venous pressure. Moreover, where a fenestration was created during the Fontan surgery, it often later becomes advisable to close the fenestration. Closing the fenestration requires another difficult catheterization procedure.
In order to gain treatment access to the heart or to make a permanent fenestration after the Fontan procedure is completed, a venous catheterization is commonly used. A catheter equipped with a puncturing or cutting tool is threaded into the graft, the desired site of the fenestration is identified, and a puncture or opening is made through the wall of the synthetic graft and into the interior of the heart. There are significant difficulties in locating the proper site for making the opening. The difficulty is further magnified by the fact that the puncture may inadvertently be made in an area not immediately adjacent the heart thereby creating a leakage into the chest cavity that is difficult if not impossible to repair. Moreover, even when the puncture is made through the graft wall and directly through the immediately adjacent and contacting outer wall of the heart, there can be difficulties due to leakage if proper sealing is not accomplished.
There is a need for a vascular tube graft that can be implanted during a Fontan procedure and which allows easy, reliable, and repeated access to the heart without creating a permanent leak or fenestration.